1. Introduction of the game:
"Plants vs. Zombies 2: It's About Time" is the highly anticipated sequel to the wildly popular "Plants vs. Zombies" game by PopCap Games. This strategy tower defense game invites players to once again protect their garden from an onslaught of quirky zombies with a variety of plant defenses. The player's mission is to grow powerful plants, supercharge them with Plant Food, and devise the ultimate plan to defend their brain.

2. All characters and levels of the game:
The game features a wide range of characters that include a colorful array of plants like the Sunflower, Peashooter, and new additions such as Bonk Choy and Laser Bean. Each plant has unique abilities and is effective against different types of zombies. The zombies are just as diverse, with the classic Conehead Zombie being joined by new adversaries like Ra Zombie and Swashbuckler Zombie. The game is structured in different worlds representing various historical and fantastical time periods, with levels ranging from Ancient Egypt and Pirate Seas to the Far Future and Jurassic Marsh, each providing their own unique challenges.

3. What attracts users most to the game:
Players are drawn to "Plants vs. Zombies 2" for its addictive gameplay, humorous tone, and the strategic depth that comes with combining different plants and strategies to counter a varied spectrum of zombie threats. The game offers a delightful mix of strategy, fast-paced action, and quirky animation, which keeps both casual and dedicated players engaged for hours. Additionally, its freemium model allows for a broad audience to enjoy the game with optional purchases for those who want to enhance their experience.

4. Why it is popular:
The game has built its popularity on the foundation of an easy-to-learn but difficult-to-master game mechanic, an imaginative art style, memorable characters, and constant updates that bring in new levels, plants, and zombies. The humor infused throughout the game, with comical plant and zombie designs and playful level scenarios, contributes significantly to its widespread appeal.

5. When the game was released and how many versions are currently available:
"Plants vs. Zombies 2" was originally released on August 15, 2013. Over the years, the game has been continually updated with new content and features. Although the core game remains the same, there have been numerous versions released—a testament to the ongoing support and enhancement the game has received to keep the player base engaged.

6. The most difficult part of the game:
One of the most challenging aspects of "Plants vs. Zombies 2" is the game's later stages and special challenge zones. These levels often push players to their limits, requiring them to make perfect use of plant synergies, timing, and resource management to survive waves of increasingly resilient and numerous zombies.

7. Strengths and weaknesses of the game:
The game's strengths lie in its engaging gameplay, variety of characters, and the depth of strategy offered by mixing and matching plant abilities. However, some users express concerns over its free-to-play model, which can sometimes make progress feel slow without in-app purchases. The difficulty spikes in later levels may also be a barrier for some casual players.

8. What other games have been developed by the same developer:
PopCap Games, the developer of "Plants vs. Zombies 2," has also developed numerous other hit games including the original "Plants vs. Zombies," "Bejeweled" series, "Peggle," "Bookworm," "Zuma," and many others. These games are known for their accessible gameplay, quirky themes, and engaging design that appeal to a broad audience.